1. Field of the Invention
The present invention relates to a fuel cell system, a fuel cell system drive method and a fuel container for power generation. More particularly, the present invention relates to a fuel reforming supply type fuel cell system which performs power generation using hydrogen gas produced from fuel for power generation and favorably applied to this fuel cell system. In addition, the present invention relates to a fuel container for power generation having a detachable structure relative to the fuel cell main body which comprises a power generation module.
2. Description of the Related Art
In recent years there has been increasing public interest in environmental problems, energy issues and global warming. As a power supply system (or power generation system) for becoming the mainstream technology of the next generation, Research and Development (R&D) has advanced rapidly toward full-scale proliferation of fuel cells. Because fuel cells discharge practically no greenhouse gases (heat-trapping gases) and air contaminants, the impact on the environment (environmental burden) is extremely low. Also, fuel cells (or a power supply system using a fuel cell) can realize extremely high generation efficiency (energy conversion efficiency) as compared with conventional power generation systems.
A power supply system for using such a fuel cell, for example, is in motor vehicles as the drive power source of an electric motor driving apparatus to replace gasoline engines and diesel engines, which have a high environmental impact due to emissions of exhaust gas, etc. Another example is in electrical power, for example, used at a business establishment, residence, etc. as low loss power generation equipment to replace electrical power from the power plant of a public utility company. Thus, practical application and commercial reality of these modern** technologies are anticipated to expand further in the years ahead.
Additionally, such fuel cell systems have been drastically miniaturized in recent years and experiments with new approaches as a power supply unit of compact electronic apparatus (portable devices), for instance, notebook type personal computers (notebook PCs), digital cameras, Personal Digital Assistants (PDAs), cellular telephones, etc. have been actively pursed.
Here, an example of a widely known fuel cell referred to as a solid polymer electrolyte membrane fuel cell will be briefly explained. In general, the power generation operation of this type of fuel cell involves the use of a solid polymer electrolyte** membrane (PEM) (polymer electrolyte fuel cell) as an electrolyte membrane (ion exchange membrane). In the electrochemical reaction, hydrogen ions and free electrons are produced from the fuel for power generation on the anode electrode side (negative pole; fuel electrode) and these hydrogen ions permeate through the electrolyte membrane layer. When combined with oxygen molecules on the cathode electrode side (positive pole; oxidizer electrode), electrical energy (electrical power) can be obtained by extracting the electrons which travel from the anode electrode side to the cathode electrode side.
As for fuel for power generation supplied to a fuel cell (anode electrode side), it is preferable to directly supply hydrogen gas. However, as for a system which supplies such hydrogen gas directly to a fuel cell, due to the technical aspects of production, storage and supply of hydrogen gas, along with the safety aspect of difficult handling and from an economic viewpoint, practical applications have been attained only in relatively large-sized systems, such as power generation equipment in a business establishment, a vehicle drive power source, etc.
On the other hand, a fuel cell system application to compact electronic apparatus (portable devices), etc. has been studied. The apparatus applies liquid hydrocarbon based fuel of the two major types: ethanol (grain-derived alcohol) and methanol** (wood- or cellulose-derived alcohol). Furthermore, procurement and handling of these two alcohols are relatively simple and the manufacturing cost necessary to produce them is economical.
Moreover, as supply systems of fuel for power generation designed to use liquid hydrocarbon based fuel in this type of fuel cell system, a fuel direct supply system which supplies the fuel for power generation (methanol, etc.) to the anode electrode of a direct fuel cell body and a fuel reforming supply system which supplies hydrogen gas obtained by reforming this fuel for power generation to the anode electrode are known.
FIG. 7 is an outline configuration diagram showing a conventional prior art solid polymer electrolyte membrane type fuel cell which uses a fuel direct supply system. FIG. 8 is an outline configuration diagram showing a conventional prior art solid polymer electrolyte membrane type fuel cell which uses a fuel reforming supply system. Here, in regard to equivalent or identical composition, the same nomenclature is appended and explained.
Initially, as seen in the outline of FIG. 7, a fuel cell body 110A has an anode electrode 111, a cathode electrode 112 and an electrolyte membrane 113. The anode electrode is composed of a carbon electrode to which predetermined catalyst molecules (for example, platinum, platinum-ruthenium, etc.) are adhered (coated) on the surface. The cathode electrode is composed of a carbon electrode to which predetermined catalyst molecules (for example, platinum, etc.) are adhered on the surface. The shape-retaining film of the electrolyte membrane 113 (ion exchange membrane) is inserted between the anode electrode 111 and the cathode electrode 112.
Also, in a fuel direct supply system such as the fuel cell body 110A configuration shown in FIG. 7, the fuel for power generation (for example, methanol CH3OH) and water H2O are directly supplied to the anode electrode 111 side and, on the opposite side, oxygen O2 in the ambient atmosphere (air) is supplied to the cathode electrode 112.
The resultant electrochemical reaction involved in the power generation operation of the fuel cell for this fuel direct supply system is as expressed in the below chemical equation (11). When methanol CH3OH is directly supplied to the anode electrode 111, the catalyst on the anode electrode 111 converts the gas to separate negatively charged electrons e− and produce positively charged hydrogen ions (protons) H+. As these hydrogen ions H+ migrate through the electrolyte membrane 113 layer to the cathode electrode 112 side, the electrons e− are extracted by the carbon electrode which constitutes the anode electrode 111 and a load LD is supplied.2CH3OH+2H2O→12H++12e−+2CO2  (11)
Also, in this chemical reaction, because water H2O is needed to promote this reaction besides methanol CH3OH, a methanol aqueous solution of several percent (%) is applied.
On the other hand, as expressed in the below chemical equation (12), by supplying air (oxygen O2) to the cathode electrode 112, the electrons e− which flow through the load LD according to the catalyzer and the hydrogen H+ ions which migrate through the electrolyte membrane 113 layer subsequently combine and react with the oxygen O2 in the air to produce water H2O as a byproduct.12H++3O2+12e−→6H2O  (12)
Such a sequence of catalytic reactions (electrochemical reactions) in the electrolyte membrane 113 composed of a solid polymer electrolyte membrane advances from ambient temperature generally in a temperature condition of around a few tens of degrees Celsius, which are relatively low temperatures. Besides producing electrical energy (electrical power), basically the only byproduct is water H2O. In addition, the electrical energy extracted by such an electrochemical reaction depends on the amount of fuel for power generation (methanol and water) supplied to the anode electrode 111 of the fuel cell body 110A.
Moreover, in a fuel reforming supply system such as the fuel cell body 110B configuration shown in FIG. 8, hydrogen gas H2 obtained by reforming the fuel for power generation (for example, methanol CH3OH) with a reformer (omitted from the diagram, but described later in detail) is supplied to the anode electrode 111 side and, on the opposite side, oxygen O2 in the ambient atmosphere (air) is supplied to the cathode electrode 112.
Accordingly, the electrochemical reaction involved in the power generation operation of the fuel cell for this fuel reforming supply system is as expressed in the below chemical equation (13). When hydrogen gas H2 is supplied to the anode electrode 111, the catalytic reaction converts the gas to separate the negatively charged electrons e− and produce positively charged hydrogen ions H+. As these hydrogen ions H+ migrate through the electrolyte membrane 113 layer to the cathode electrode 112 side, the electrons e− are extracted by the carbon electrode which constitutes the anode electrode 111 and a load LD is supplied.2H2→4H++4e−  (13)
On the other hand, as expressed in the below chemical equation (14), by supplying air (oxygen O2) to the cathode electrode 112, the electrons e− which flow through the load LD according to the catalyzer and the hydrogen H+ ions which migrate through the electrolyte membrane 113 layer subsequently combine and react with the oxygen O2 in the air to produce water H2O as a byproduct.4H++O2+4e−→2H2O  (14)
Such a sequence of electrochemical reactions ((13) type and (14) type) advances in temperature conditions of generally 60˜80° C. (140˜176° F.), which are relatively low temperatures. Besides producing electrical energy (electrical power), basically the only byproduct is water H2O. In addition, the electrical energy extracted by such an electrochemical reaction depends on the amount of hydrogen gas H2 supplied to the anode electrode 111 of the fuel cell body 110B.
Apart from that, in the power generation operation in the fuel cell of each the fuel supply systems mentioned above, the conduction (migration) of hydrogen ions H+ in the electrolyte membrane layer is in the form of H3O+ hydronium ions (hydrated ions) which combines water H2O (moisture) with the hydrogen ions H+. Thus, to promote the above-mentioned electrochemical reaction and to increase power generation efficiency, it is known that it is necessary to make the ambient atmosphere near the electrolyte membrane into a water vapor hydrated state (wet/damp state). A power generation operation of such a fuel cell, for example, has been disclosed in the details of Japanese Laid-Open (Kokai) Patent Application No. 2004-178889 titled “FUEL CELL SYSTEM.”
Here, as mentioned above, in a fuel cell of a fuel direct supply system, the ambient atmosphere near the electrolyte can be made into a sufficient water vapor hydrated state by directly supplying a methanol aqueous solution which constitutes the fuel for power generation (methanol, etc.) and water to the anode electrode 111. In view of that, the electrochemical reaction related to the above-described power generation operation can be satisfactorily accelerated. Moreover, in a fuel cell of this method, the configuration of the fuel cell system can be simplified. However, in general, as compared with a fuel cell of a fuel reforming supply system, there is a problem that generation efficiency (energy conversion efficiency) is lower.
On the other hand, in a fuel cell of a fuel reforming supply system, when attention is directed only to the electrochemical reaction related to the power generation operation mentioned above, water H2O (moisture) is not needed. Thus, a means is necessary, such as a humidifier, etc., for making the ambient atmosphere near the electrolyte into a sufficient water vapor hydrated state (wet state). Notably, it is necessary to provide a reformer for reforming fuel for power generation (methanol, etc.) and producing hydrogen gas H2. Also, the configuration of the fuel cell system is complicated. However, in general, as compared with a fuel cell of a fuel direct supply system, the fuel cell of this method has the characteristic that generation efficiency (energy conversion efficiency) is higher.
Therefore, when a fuel cell system is installed as the power supply unit in a portable type electronic apparatus in which drastic miniaturization is not necessary, such as a cellular telephone device, portable audio equipment, etc. according to neither the display panel size (screen) nor the matter of user-friendliness of the input device (keyboard, etc.), etc. like a notebook PC, PDA, etc. or in an apparatus where miniaturization is not so important, it is more preferable to apply a fuel cell system of a fuel reforming supply system which has superior generation efficiency. This is the case even though drastic miniaturization cannot be performed more than a fuel cell system of a fuel direct supply system which can be miniaturized, but has inferior generation efficiency.
As stated above, with regard to the fuel cell system of a fuel reforming supply system, in order to accelerate the electrochemical reaction related to the power generation operation in a fuel cell body, it is necessary to maintain the electrolyte membrane (ion exchange membrane) in a wet state. For maintaining a wet state, for example in the conventional prior art mentioned above in JP 2004-178889, a configuration has been proposed in which the water produced as a byproduct upon power generation operation in the fuel cell body (namely, the electrochemical reaction ion exchange membrane composing the chemical equations (13) and (14)) is recovered and supplied in close proximity to the electrolyte membrane.
However, as for the electrochemical reaction related to the power generation operation in the fuel cell body, in order to recover water produced as a byproduct and to supply the electrolyte membrane of the fuel cell body, the above-described power generation operation needs to be stably executed.
In view of that, with regard to the power generation operation where the electrochemical reaction composing the chemical equations (13) and (14) is steadily accelerated after the power generation operation has been started, although the fuel cell can recover water produced as a byproduct, supply the electrolyte membrane and maintain a predetermined wet state, there is a drawback. Specifically, there is a problem that the electrolyte membrane cannot be adequately maintained in a predetermined wet state as the water produced as a byproduct is recovered upon a power generation operation start-up or immediately after the start-up (upon system start-up).
As a method of solving such a problem, for example, although humidifying the electrolyte membrane in advance to a water vapor hydrated state before shipment of electronic apparatus containing a fuel cell system, etc. has been considered, there are still other related problems. Notably, after shipment of the electronic apparatus, the electrolyte membrane rapidly dries out due to climate conditions, etc., thus power generation operation becomes impossible. Also, there is a possibility of an operational malfunction in which the electrolyte layer is destroyed by freezing which produces a defective system. Hence, environmental management (especially, temperature and humidity management) at the time of shipping, storage and equipment stoppage must be strictly enforced.